I see that utilitarian has already made this point:

Summary. In many cases, the good accomplished by money is approximately proportional to the amount donated, so that traditional arguments for being risk averse with respect to wealth don't apply. In such circumstances, utilitarians should take advantage of economic risk premia, such as those that accrue to riskier stocks. (For instance, in the context of the Capital Asset Pricing Model, "riskier" means "higher beta," i.e., higher scaled covariance with market returns.)